This invention relates generally to fault indicators, and more particularly to non-self resetting fault indicators which include user-actuable reset means, such as described in U.S. Pat. Nos. 3,413,548 and 4,086,529 of the present inventor. This invention constitutes an improvement in such fault indicators.
Fault indicators are generally installed on conductors in commercial electrical power distribution systems. In such distribution systems a short circuit, or fault, may develop, resulting in loss of service to consumers. Following the occurrence of such a fault it is necessary that the fault be quickly located and repaired to enable service to be restored.
Fault indicators are typically installed on a conductor and are constructed in such a manner that when the current flowing through the conductor exceeds a predetermined level an indicator is tripped to a fault-indicating state to indicate that such excessive current has occurred. Fault indicators placed on conductors which do not experience a fault current remain in an untripped or reset-indicating state. By systematically inspecting the fault indicators located at various points in the power distribution system, the fault can be quickly located and repaired.
Generally when a fault occurs within a power distribution system a circuit breaker in the system trips, cutting off current to a portion of the system. Since no current flows in affected conductors in the system, fault indicators for use in such systems are constructed in such a manner that an indication of the excessive current flow remains following the occurrence of the fault, even through the current immediately following the fault may have dropped to zero. A fault indicator in such a condition is said to be in a "tripped" state, and is no longer able to indicate the occurrence of a subsequent fault current. In order to make the indicator operative once again, it is necessary that the indicator be reset to a "reset" state.
One form of prior manually-reset fault indicator, as described in U.S. Pat. No. 3,413,548, utilized a rotatably mounted bi-stable indicator flag having reset-indicating and fault-indicating positions to visually indicate tripped and reset states. This fault indicator was reset by means of a reset tool having a permanent magnet which was positioned in close proximity to the fault indicator by a lineman to magnetically reposition the indicator flag to its reset position. This was often a cumbersome process, in that it was necessary for the lineman to carry a special reset tool, and to accurately position the tool relative to the indicator housing in an often dark and cramped environment. This was particularly disadvantageous where it was necessary to individually reset a large number of fault indicators, since the burden in the reset procedure was multiplied many times over.
In another form of prior manually-reset fault indicators, as described in U.S. Pat. No. 4,086,529, the indicator flag was positioned to its fault-indicating position by a pole piece magnetized by the fault current, and repositioned to its reset-indicating position by a reset tool having a magnetic winding which remagnetized the pole piece. This also required accurate placement of the reset tool.
Another prior fault indicator utilized a spring-biased indicator flag which was mechanically latched upon reaching a fault-indicating position. Reset was accomplished by displacing the latch to allow the spring to return the indicator flag to its reset position.
Another prior fault indicator provided a permanent magnet externally mounted to the indicator housing which could be pivoted or otherwise positioned so as to interact with the indicator flag to reposition the indicator to its reset position. The arrangement had the disadvantage of being bulky, expensive, and prone to mechanical breakdown.
Thus a need exists for a fault indicator having simple, reliable self-contained user-actuable reset means, which avoids the disadvantages of prior constructions.
Accordingly, it is an object of this invention to provide a new and improved user-resettable fault indicator.
It is another object of the present invention to provide a self-contained manually-resettable fault indicator which can be conveniently reset without the need for external reset tools.